Micro concave-convex structure for optical body and display device

ABSTRACT

There is provided an optical body and a display device that enable wavelength dependence of a reflectance to be reduced and reflection of incident light to be further suppressed, the optical body including: a concave-convex structure formed on a surface of a base material. An average period of concavities and convexities of the concave-convex structure is equal to or shorter than a wavelength belonging to a visible light band. A standard deviation of differences between respective positions of bottom faces of the concavities of the concave-convex structure in a normal direction of a flat surface of the base material and a median of the positions of the bottom faces is greater than or equal to 25 nm.

CROSS REFERENCE TO PRIOR APPLICATION

This application is a National Stage Patent Application of PCTInternational Patent Application No. PCT/JP2016/079542 (filed on Oct. 4,2016) under 35 U.S.C. § 371, which claims priority to Japanese PatentApplication No. 2015-215135 (filed on Oct. 30, 2015), which are allhereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates to an optical body and a display device.

BACKGROUND ART

Optical bodies having various characteristics are generally provided ona surface on which light is incident in a display device such as atelevision and an optical element such as a camera lens for the purposeof controlling transmission of light.

As such an optical body, for example, an optical body having a microconcave-convex structure (a so-called moth-eye structure) formed on asurface of which an average period of concavities and convexities isequal to or shorter than a wavelength belonging to a visible light bandcan be exemplified. Since a refractive index of the surface on which themicro concave-convex structure is formed gently changes with respect toincident light, an abrupt change in the refractive index, which is thecause of reflection, does not occur. Thus, an optical body having themicro concave-convex structure formed on a light incidence surface canreduce reflection of incident light over a wide wavelength band.

For example, Patent Literature 1 described below discloses ananti-reflective laminate having the micro concave-convex structureformed on a surface using an anodic oxidation method. In addition,Patent Literature 2 described below discloses a technology of producingan optical element by forming an inverted shape of the microconcave-convex structure on a master using lithography and etching andtransferring the inverted shape formed on the master to a resinmaterial.

In addition, Patent Literature 3 described below discloses an opticalmember having a concave-convex structure formed on a surface by directlyperforming dry etching on a base material without using a mask in orderto alleviate wavelength dependence of a reflectance.

CITATION LIST Patent Literature

Patent Literature 1: JP 2009-230045A

Patent Literature 2: JP 2009-258751A

Patent Literature 3: JP 2013-109228A

SUMMARY OF INVENTION Technical Problem

However, such optical bodies produced in the technologies disclosed inPatent Literature 1 and Patent Literature 2 have a problem that areflectance thereof fluctuates depending on a wavelength of incidentlight. The reason for this is that, since the micro concave-convexstructure with concavities and convexities having substantially uniformheights is formed in the technologies disclosed in Patent Literature 1and Patent Literature 2, the micro concave-convex structure is notcapable of dealing with incident light beams having various wavelengths.

In addition, there is a problem with the optical member disclosed inPatent Literature 3 that, since a reflectance of the optical member isset to be high, it is not possible to obtain a satisfactory reflectionsuppression effect.

Thus, the present invention takes the above-described problems intoaccount and aims to provide a novel and improved optical body anddisplay device that enable wavelength dependence of a reflectance to bereduced and reflection of incident light to be further suppressed.

Solution to Problem

According to an aspect of the present invention in order to achieve theabove object, there is provided an optical body including: aconcave-convex structure formed on a surface of a base material. Anaverage period of concavities and convexities of the concave-convexstructure is equal to or shorter than a wavelength belonging to avisible light band. A standard deviation of differences betweenrespective positions of bottom faces of the concavities of theconcave-convex structure in a normal direction of a flat surface of thebase material and a median of the positions of the bottom faces isgreater than or equal to 25 nm.

A standard deviation of differences between respective positions ofvertexes of the convexities of the concave-convex structure in thenormal direction of the flat surface of the base material and a medianof the positions of the vertexes may be greater than or equal to 35 nm.

A Y value that is a luminous reflectance of the optical body may beequal to or lower than 0.2%, and the absolute values of reflection huesa* and b* of the optical body may be equal to or smaller than 1.

An average reflectance of the optical body in a wavelength band from 380nm to 780 nm may be equal to or lower than 0.2%.

A macro concave-convex structure formed on the surface of the basematerial to be superimposed on the concave-convex structure may befurther included. An average period of concavities and convexities ofthe macro concave-convex structure may be longer than a wavelengthbelonging to the visible light band.

A planar array of the convexities or concavities of the concave-convexstructure may be a hexagonal grid shape or a square grid shape.

A planar array of the convexities or concavities of the concave-convexstructure may be a random array.

According to another aspect of the present invention in order to achievethe above object, there is provided a display device including: theabove optical body.

According to the present invention, since it is possible to increaseunevenness in positions of bottom faces of concavities of a microconcave-convex structure in a normal direction of a flat surface of abase material, the micro concave-convex structure can suppressreflection of incident light beams having various wavelengths.

Advantageous Effects of Invention

According to the present invention described above, the wavelengthdependence of a reflectance of an optical body can be reduced andreflection of incident light can be further suppressed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional diagram schematically illustrating across-sectional shape obtained by cutting an optical body according toan embodiment of the present invention in a thickness direction.

FIG. 2 is an enlarged cross-sectional diagram schematically illustratingan enlarged partial region X of FIG. 1.

FIG. 3 is a cross-sectional diagram schematically illustrating across-sectional shape obtained by cutting an optical body according to amodified example in a thickness direction.

FIG. 4 is a perspective diagram schematically illustrating a master usedin producing an optical body according to an embodiment of the presentinvention.

FIG. 5 is a schematic diagram for describing a production method of amaster.

FIG. 6 is a schematic diagram for describing pulse signals generated bya control mechanism.

FIG. 7 is an explanatory diagram for describing a specific configurationof an exposure device used in exposure of a master base material tolight.

FIG. 8 is a schematic diagram illustrating a configuration of a transferdevice producing an optical body according to an embodiment of thepresent invention.

FIG. 9 is a perspective diagram expressing a surface shape of an opticalbody according to Example 2 measured using an AFM.

FIG. 10 is a graph chart in which reflectances of optical bodiesaccording to Examples 1 to 3 and Comparative Examples 1 and 2 areevaluated at each wavelength of incident light.

FIG. 11 is a scatter diagram illustrating correlations between standarddeviations of differences between positions of bottom faces ofconcavities of optical bodies and a median of the positions of thebottom faces and Y values of the optical bodies.

FIG. 12 is a graph chart in which reflectances of optical bodiesaccording to Example 4 and Comparative Example 3 are evaluated at eachwavelength of incident light.

DESCRIPTION OF EMBODIMENTS

Hereinafter, (a) preferred embodiment(s) of the present invention willbe described in detail with reference to the appended drawings. Notethat, in this specification and the appended drawings, structuralelements that have substantially the same function and structure aredenoted with the same reference numerals, and repeated explanation ofthese structural elements is omitted.

<1. Structure of Optical Body>

First, a structure of an optical body according to an embodiment of thepresent invention will be described with reference to FIG. 1 and FIG. 2.FIG. 1 is a cross-sectional diagram schematically illustrating across-sectional shape obtained by cutting an optical body 1 according tothe present embodiment in a thickness direction.

The optical body 1 has a micro concave-convex structure 13 formed on asurface of a base material 11 as illustrated in FIG. 1.

The base material 11 is a transparent material. The base material 11 maybe, for example, a transparent resin substrate of polycarbonate,polyethylene terephthalate, polymethyl methacrylate, or the like, atransparent resin film of cellulose triacetate (TAC), a cyclic olefincopolymer (COC), or the like, or a transparent glass substrate of quartzglass, soda-lime glass, lead glass, or the like. However, the basematerial 11 is not limited to the above-described materials, and may beanother known transparent material.

Note that the above-mentioned “transparent” means a high transmittanceof light having a wavelength belonging to a visible light band(approximately from 360 nm to 830 nm). Being “transparent” may mean, forexample, having a transmittance of 70% or higher for light having awavelength belonging to the visible light band.

The micro concave-convex structure 13 is a concave-convex structureformed on the base material 11. The micro concave-convex structure 13has convexities 131 that are convex with respect to a flat surface 12 ofthe base material 11 and concavities 133 that are concave with respectto the flat surface 12 of the base material 11.

An average period of the concavities and convexities of the microconcave-convex structure 13 is equal to or shorter than a wavelengthbelonging to the visible light band (e.g., equal to or shorter than 830nm), and is preferably larger than or equal to 100 nm and equal to orshorter than 350 nm. Here, the average period of the concavities andconvexities of the micro concave-convex structure 13 means an averagedistance between the vertexes of adjacent convexities 131 or an averagedistance between the centers of bottom faces of adjacent concavities133. Since a refractive index of the surface of the base material 11 onwhich the micro concave-convex structure 13 is formed gently changeswith respect to incident light, an abrupt change in a refractive index,which is the cause of reflection, does not occur. For this reason, themicro concave-convex structure 13 can lower a reflectance of the basematerial 11 with respect to incident light in a wide wavelength bandincluding visible light.

The planar array of the micro concave-convex structure 13 may be, forexample, a two-dimensional array in which the convexities 131 or theconcavities 133 are periodically arrayed on a plane parallel to the flatsurface of the base material 11, or may be a random two-dimensionalarray with no periodicity. In the case in which the convexities 131 orthe concavities 133 of the micro concave-convex structure 13 areperiodically arrayed, the two-dimensional array pattern of theconvexities 131 or the concavities 133 may be a hexagonal grid patternor a square grid pattern.

In addition, in the case in which the two-dimensional array pattern ofthe convexities 131 or the concavities 133 is a hexagonal grid or squaregrid pattern, a distance (which is also called a pitch) between therespective convexities 131 or concavities 133 may be, for example,longer than or equal to 100 nm and equal to or shorter than 350 nm, orpreferably longer than or equal to 150 nm and equal to or shorter than280 nm. A case in which the distance between the respective convexities131 or concavities 133 is shorter than 100 nm is not desirable becauseforming the micro concave-convex structure 13 can be difficult. Inaddition, a case in which the distance between the respectiveconvexities 131 or concavities 133 exceeds 350 nm is not desirablebecause there is a possibility of diffraction of visible light. Notethat the distance between the respective convexities 131 or concavities133 may vary depending on an arrangement direction or may be uniform.

Here, although not illustrated, in a case in which positions of bottomfaces of the concavities 133 of the micro concave-convex structure 13 inthe normal direction of the flat surface 12 of the base material 11 aresubstantially uniform as disclosed in the related art, the reflectanceof the base material 11 with respect to incident light has wavelengthdependence in accordance with depths of the concavities 133. Since suchan optical body deals with a significantly high ratio of reflected lighthaving a wavelength that causes a relatively high reflectance, thereflected light has a color (i.e., the reflected light contains a hue).In addition, a Y value that is a luminous reflectance increases in awavelength band that causes a relatively high reflectance.

On the other hand, in the optical body 1 according to the presentembodiment, the positions of the bottom faces of the concavities 133 ofthe micro concave-convex structure 13 in the normal direction of theflat surface 12 of the base material 11 are uneven over a certain degreeas illustrated in FIG. 1. Accordingly, the optical body 1 according tothe present embodiment can suppress reflection of light beams havingvarious wavelengths, and thus can reduce wavelength dependence ofreflectance. Therefore, the optical body 1 according to the presentembodiment can suppress reflection of incident light without causingreflected light to have a color.

Next, a structure of the micro concave-convex structure 13 will bedescribed in more detail with reference to FIG. 2. FIG. 2 is an enlargedcross-sectional diagram schematically illustrating an enlarged partialregion X of FIG. 1.

The positions of the bottom faces of the concavities 133 in the normaldirection of the flat surface 12 of the base material 11 are uneven inthe micro concave-convex structure 13 of the optical body 1 according tothe present embodiment as illustrated in FIG. 2. Specifically, thestandard deviation of the differences between the respective positionsof the bottom faces of the concavities 133 in the normal direction ofthe flat surface 12 of the base material 11 and the median of thepositions of the bottom faces of the concavities 133 is greater than orequal to 25 nm. In the case in which a value of the unevenness in thepositions of the bottom faces of the concavities 133 of the microconcave-convex structure 13 is greater than or equal to theabove-mentioned value, the wavelength dependence of the reflectance ofthe optical body 1 can be dramatically reduced.

Note that an upper limit value of the standard deviation of thedifferences between the positions of the bottom faces of the concavities133 and the median of the positions of the bottom faces is notparticularly limited. However, in a case in which the standard deviationis very large exceeding 25 nm, there is a risk of the effect of reducingthe wavelength dependence being saturated and other opticalcharacteristics being affected. Thus, the upper limit value of thestandard deviation of the differences between the positions of thebottom faces of the concavities 133 and the median of the positions ofthe bottom faces can be set to 200 nm.

Here, a method of calculating the above-described standard deviation ofthe differences between the respective positions of the bottom faces ofthe concavities 133 and the median of the positions of the bottom facesof the concavities 133 will be described in more detail with referenceto FIG. 2.

First, a surface shape of a predetermined region (e.g., 2 square μm, orthe like) of the optical body 1 is measured using an atomic forcemicroscope (AFM), or the like. Next, after a cross-sectional shape ofthe micro concave-convex structure 13 is calculated using the measuredsurface shape, the respective positions of the bottom faces of theconcavities 133 in the normal direction of the flat surface 12 of thebase material 11 are measured. At this time, each of the positions ofthe bottom faces of the concavities 133 may be measured by setting, forexample, the position of the bottom face of a concavity 133B that isclosest to the flat surface 12 side of the base material 11 as a zeropoint (a reference point).

Next, the median (also called a median value) of the positions of thebottom faces of the concavities 133 in the normal direction of the flatsurface 12 of the base material 11 is calculated. Accordingly, thestandard deviation of the differences between the respective positionsof the bottom faces of the concavities 133 in the normal direction ofthe flat surface 12 of the base material 11 and the median of thepositions of the bottom faces can be calculated. Note that, in FIG. 2,the median of the positions of the bottom faces of the concavities 133is denoted by Bm. In addition, the position of the bottom face of aconcavity 133A that is farthest from the flat surface 12 side of thebase material 11 is denoted by Ba, and the position of the bottom faceof the concavity 133B that is closest to the flat surface 12 side of thebase material 11 is denoted by Bb.

In addition, in the micro concave-convex structure 13 of the opticalbody 1 according to the present embodiment, it is desirable for thepositions of the vertexes of the convexities 131 in the normal directionof the flat surface 12 of the base material 11 to be uneven asillustrated in FIG. 2. Specifically, it is desirable for the standarddeviation of the differences between the respective positions of thevertexes of the convexities 131 in the normal direction of the flatsurface 12 of the base material 11 and the median of the positions ofthe vertexes of the convexities 131 to be greater than or equal to 35nm. In the case in which a value of unevenness of the positions of thevertexes of the convexities 131 of the micro concave-convex structure 13is greater than or equal to the above-mentioned value, the wavelengthdependence of the reflectance of the optical body 1 can be furtherreduced.

Note that an upper limit of the standard deviation of the differencesbetween the positions of the vertexes of the convexities 131 and themedian of the positions of the vertexes is not particularly limited.However, in a case in which the standard deviation is very largeexceeding 35 nm, there is a risk of the effect of reducing thewavelength dependence being saturated and other optical characteristicsbeing affected. Thus, the upper limit value of the standard deviation ofthe differences between the positions of the vertexes of the convexities131 and the median of the positions of the vertexes may be set to 200nm.

The standard deviation of the differences between the respectivepositions of the vertexes of the convexities 131 and the median of thepositions of the vertexes of the convexities 131 can also be calculatedsimilarly to that with respect to the positions of the bottom faces ofthe concavities 133.

First, the surface shape of a predetermined region (e.g., 2 square μm)of the optical body 1 is similarly measured using an AFM or the like,and after a cross-sectional shape of the micro concave-convex structure13 is calculated, the respective positions of the vertexes of theconvexities 131 in the normal direction of the flat surface 12 of thebase material 11 are measured. At this time, the respective positions ofthe vertexes of the convexities 131 may be measured by setting, forexample, the position of the bottom face of the concavity 133B that isclosest to the flat surface 12 side of the base material 11 as a zeropoint (a reference point).

Next, the median (also called a median value) of the positions of thevertexes of the convexities 131 in the normal direction of the flatsurface 12 of the base material 11 is calculated. Accordingly, thestandard deviation of the differences between the respective positionsof the vertexes of the convexities 131 in the normal direction of theflat surface 12 of the base material 11 and the median of the positionsof the vertexes can be calculated. Note that, in FIG. 2, the median ofthe positions of the vertexes of the convexities 131 is denoted by Tm.In addition, the position of the vertex of a convexity 131A that isfarthest from the flat surface 12 side of the base material 11 isdenoted by Ta, and the position of the vertex of the convexity 131B thatis closest to the flat surface 12 side of the base material 11 isdenoted by Tb.

Here, the difference between the median Tm of the positions of thevertexes of the convexities 131 and the median Bm of the positions ofthe bottom faces of the concavities 133 is an average height h of theconvexities 131 of the micro concave-convex structure 13. The averageheight h of the convexities 131 of the optical body 1 according to thepresent embodiment may be, for example, higher than or equal to 100 nmand equal to or lower than 400 nm, or preferably higher than or equal to200 nm and equal to or lower than 300 nm.

The optical body 1 having the above-described structure can reduce thewavelength dependence of the reflectance. Specifically, the optical body1 according to the present embodiment can have the absolute values ofreflection hues (a*, b*) equal to or smaller than 1. Reflection hues(a*, b*) are (L*, a*, b*) when the color of reflected light is expressedin a L* a* b* color system and represent that the color of reflectedlight is closer to white as the values of the reflection hues (a*, b*)of the reflected light get closer to 0. Thus, since the optical body 1according to the present embodiment can reduce the wavelength dependenceof the reflectance, it can cause reflected light not to have a color.

In addition, the optical body 1 having the above-described structure cansuppress reflection of incident light more. Specifically, the opticalbody 1 according to the present embodiment can have a Y value that is aluminous reflectance equal to or lower than 0.2%. The Y value (luminousreflectance) is (Y, x, y) when the color of reflected light is expressedin a Yxy color system and represents that reflection is suppressedfurther as the Y value (luminous reflectance) becomes smaller. Thus, theoptical body 1 according to the present embodiment can further suppressreflection of incident light.

In addition, the optical body 1 having the above-described structureparticularly can suppress reflection of light having a wavelengthbelonging to the visible light band. Specifically, the optical body 1according to the present embodiment can have an average reflectanceequal to or lower than 0.2% in the wavelength band from 380 nm to 780nm. Accordingly, in a case in which the optical body 1 according to thepresent embodiment is used for a display surface of a display device orthe like, the optical body can suppress reflection of light having awavelength belonging to the visible light band visible to humans. Thus,the optical body 1 according to the present embodiment can remarkablyimprove visibility of a display device or the like.

2. Modified Example

Next, a modified example of the optical body according to the presentembodiment will be described with reference to FIG. 3. FIG. 3 is across-sectional diagram schematically illustrating a cross-sectionalshape obtained by cutting an optical body 1A according to the presentmodified example in a thickness direction.

The optical body 1A has a macro concave-convex structure 14 formed in asuperimposing manner with the micro concave-convex structure 13 inaddition to the micro concave-convex structure 13 formed on a surface ofthe base material 11 as illustrated in FIG. 3.

Since a material of the base material 11 of the optical body 1Aaccording to the present modified example is substantially similar tothat of the optical body 1 illustrated in FIG. 1, description thereofwill be omitted here.

In addition, an average period of concavities and convexities of themicro concave-convex structure 13 of the optical body 1A is equal to orshorter than a wavelength belonging to the visible light band (e.g.,equal to or shorter than 830 nm) as well. Furthermore, the standarddeviation of the differences between respective positions of bottomfaces of the concavities 133 of the micro concave-convex structure 13 inthe normal direction of a flat surface 12 of a base material 11 and themedian of the positions of the bottom faces of the concavities 133 isgreater than or equal to 25 nm.

The macro concave-convex structure 14 have peaks 141 that areconvexities with respect to the flat surface 12 of the base material 11and valleys 143 that are concavities with respect to the flat surface 12of the base material 11. An average period of the concavities andconvexities of the macro concave-convex structure 14 is larger than awavelength belonging to the visible light band (e.g., exceeding 830 nm),or preferably greater than or equal to 1 μm and equal to or shorter than100 μm. Here, the average period of the concavities and convexities ofthe macro concave-convex structure 14 is an average distance betweenadjacent peaks 141 or valleys 143.

The above-described macro concave-convex structure 14 may have a roughsurface structure in which, for example, the average period of theconcavities and convexities is greater than or equal to 1 μm and equalto or shorter than 100 μm. Because the macro concave-convex structure 14can scatter light incident on the surface of the base material 11, anantiglare effect can be imparted to the optical body 1A. Thus, becausethe optical body 1A according to the present modified example has areflection suppression effect attributable to the micro concave-convexstructure 13 and an antiglare effect attributable to the macroconcave-convex structure 14, the optical body can remarkably improvevisibility of a display surface when the optical body is used for adisplay surface of a display device or the like.

<3. Production Method of Optical Body>

Next, a production method of the optical body 1 according to the presentembodiment will be described with reference to FIG. 4 to FIG. 8. FIG. 4is a perspective diagram schematically illustrating a master 2 used inproducing the optical body 1 according to the present embodiment.

The optical body 1 according to the present embodiment can be producedusing, for example, a roll-to-roll nano-imprinting method using themaster 2 illustrated in FIG. 4.

The roll-to-roll nano-imprinting method specifically is a method oftransferring a concave-convex structure formed on an outercircumferential surface of the master to a resin base material or thelike by pressing the master with the concave-convex structure formed onthe outer circumferential surface on the base material or the like whilerotating the master. The optical body 1 according to the presentembodiment can be efficiently produced by, for example, pressing themaster with the micro concave-convex structure 13 formed on the outercircumferential face to the base material 11 while rotating the master.

The master 2 for producing the optical body 1 according to the presentembodiment is formed of, for example, a cylindrical or columnar masterbase material 21 having an outer circumferential surface with aconcave-convex structure 23 formed thereon as illustrated in FIG. 4.

The master base material 21 is, for example, a cylindrical or columnarmember. A shape of the master base material 21 may be a hollow cylindershape having a hollow therein as illustrated in FIG. 4 or a solidcolumnar shape with no cavity therein. A material of the master basematerial 21 is not particularly limited, and quartz glass (SiO₂) such asfused quartz glass, synthetic quartz glass, or the like, a metal such asstainless steel or the like, a material of which an outercircumferential surface of a metal such as stainless steel or the likeis coated with SiO₂, or the like can be used.

Although a size of the master base material 21 is not particularlylimited, a length thereof in an axial direction may be, for example,longer than or equal to 100 mm, and an outer diameter thereof may belarger than or equal to 50 mm and equal to or smaller than 300 mm. Inaddition, in the case in which the master base material 21 has acylindrical shape, a thickness of the cylinder may be larger than orequal to 2 mm and equal to or smaller than 50 mm.

The concave-convex structure 23 is a structure in which the structure isformed on the outer circumferential surface of the master base material21 and the micro concave-convex structure 13 formed on the surface ofthe optical body 1 is inverted. Since the concave-convex structure 23has the structure in which the micro concave-convex structure 13 isinverted, an average period of concavities and convexities of theconcave-convex structure 23 is equal to or shorter than a wavelengthbelonging to the visible light band (e.g., equal to or shorter than 830nm), similarly to that of the micro concave-convex structure 13. Inaddition, positions of bottom faces of concavities and positions ofvertexes of convexities of the concave-convex structure 23 havepredetermined unevenness in the normal direction of the outercircumferential surface of the master base material 21 as describedabove.

Note that a planar array of the concave-convex structure 23 may be, forexample, a two-dimensional array in which the convexities andconcavities are periodically arrayed or a random two-dimensional arrayin which the convexities and concavities have no periodicity. Theconvexities or concavities of the concave-convex structure 23 may bearrayed in, for example, a hexagonal grid shape or a square grid shape.

Next, a production method of the master 2 will be described withreference to FIGS. 5 to 7. FIG. 5 is a schematic diagram for describingthe production method of the master 2.

The master 2 can be produced by sequentially executing, for example, afilm formation process of forming a resist layer formed of an inorganicmaterial on the outer circumferential surface of the master basematerial 21, an exposure process of forming a latent image on the resistlayer by irradiating the resist layer with laser light, a developmentprocess of developing the resist layer with the latent image formedthereon, and an etching process of forming the concave-convex structure23 on the outer circumferential surface of the master base material 21by performing etching using the resist layer having a pattern formedthrough the development as a mask.

First, in the film formation process, a resist layer formed of aninorganic material is formed on the outer circumferential surface of themaster base material 21. As the inorganic material for forming theresist layer, for example, a metal oxide containing one or two or morekinds of transition metals such as tungsten, molybdenum, or the like canbe used. The resist layer can be formed using, for example, a sputteringmethod.

Next, latent images 23A corresponding to the concave-convex structure 23are formed on the resist layer in the exposure process by irradiatingthe resist layer formed on the outer circumferential surface of themaster base material 21 with layer light 30 emitted from an exposuredevice 3 as illustrated in FIG. 5.

Next, in the development process, a resist pattern corresponding to thelatent image 23A is formed on the resist layer by developing the resistlayer having the latent images 23A formed thereon. In a case in whichthe resist layer is formed of an inorganic material, for example, theresist layer is developed using an alkaline solution such as atetramethylammonium hydroxide (TMAH) aqueous solution.

Next, in the etching process, the concave-convex structure 23corresponding to the latent images 23A is formed on the outercircumferential surface of the master base material 21 by etching themaster base material 21 using the resist layer having the resist patternformed thereon as a mask. For the etching of the master base material21, any of dry etching or wet etching can be used. In a case in which amaterial of the master base material 21 is quartz glass (SiO₂), forexample, the master base material 21 can be etched in dry etching usingfluorocarbon gas or in wet etching using hydrofluoric acid or the like.

In the production method of the master 2 according to the presentembodiment, the above-described concave-convex structure 23 can beformed on the outer circumferential surface of the master base material21 by appropriately controlling irradiation of the laser light 30 fromthe exposure device 3 in the exposure process. The exposure device 3used in the production method of the master 2 according to the presentembodiment will be described below with reference to FIG. 5.

The exposure device 3 includes a laser light source 31 that emits thelaser light 30 and a control mechanism 47 that controls oscillation ofthe laser light 30 from the laser light source 31 as illustrated in FIG.5.

The laser light source 31 is a light source that emits the laser light30. The laser light source 31 may be of, for example, a semiconductorlaser or the like. Although a wavelength of the laser light 30 emittedby the laser light source 31 is not particularly limited, it may be, forexample, a wavelength in the range from 400 nm to 500 nm in a blue lightband.

The control mechanism 47 generates a control signal for controllingoscillation made by the laser light source 31. By generating a pulsesignal having randomness, the control mechanism 47 can impart randomness(i.e., unevenness) to a disposition and height of the concave-convexstructure 23 in a wavelength region of visible light or further. Here,the pulse signal having randomness may be specifically a randomlyphase-modulated pulse signal or a random signal (including apseudo-random signal).

The exposure device 3 performs irradiation of the laser light 30 on, forexample, the master base material 21 rotating with respect to an axiswhile moving the irradiation position of the laser light 30 in the axialdirection of the master base material 21 (the direction of the arrow R).Accordingly, the master base material 21 is exposed to light by theexposure device 3 in a spiral shape and thereby the latent images 23Aare formed.

Here, pulse signals having randomness generated by the control mechanism47 will be described in detail with reference to FIG. 6. FIG. 6 is aschematic diagram for describing pulse signals generated by the controlmechanism 47.

The pulse signal illustrated in (A) of FIG. 6 is a periodic rectangularwave having a period of P and a pulse width of D. In a case in which thecontrol mechanism 47 generates the pulse signal illustrated in (A) ofFIG. 6, for example, lengths of an irradiation time and anon-irradiation time of the laser light 30 are uniform. Thus, sincesizes of regions of the resist layer thermally reacting due to theexposure become periodic as well, the periodic latent images 23A areformed on the resist layer. Hence, open regions formed due to thedissolved resist and regions in which the resist remains having uniformsizes are periodically arranged on the developed resist layer, and thusthe master base material 21 has concavities having uniform depths andconvexities having uniform heights formed thereon through etching.

Meanwhile, the control mechanism 47 generates a pulse signal havingrandomness as illustrated in (B) or (C) of FIG. 6 in the presentembodiment.

The pulse signal illustrated in (B) of FIG. 6 is a rectangular wavehaving random periods of P1, P2, P3, P4, . . . and random pulse widthsof D1, D2, D3, D4, . . . . In a case in which the control mechanism 47generates the pulse signal illustrated in (B) of FIG. 6, for example,lengths of an irradiation time and a non-irradiation time of the laserlight 30 become random. Thus, since sizes of regions of the resist layerthermally reacting due to the exposure randomly vary depending onirradiation quantities of the laser light 30, the latent images 23Ahaving the random sizes are formed on the resist layer. Hence, openedregions formed due to the dissolved resist and regions in which theresist remains having the random sizes are arranged on the developedresist layer, and thus the master base material 21 has concavitieshaving uneven depths and convexities having uneven heights formedthereon through etching.

The optical body 1 produced using the master 2 having the concave-convexstructure 23 formed thereon using such a random pulse signal has thestandard deviation of the differences between the respective positionsof the bottom faces of concavities 133 in the normal direction of theflat surface 12 of the base material 11 of the optical body 1 and themedian of the positions of the bottom faces of the concavities 133greater than or equal to 25 nm as described above. In addition, theoptical body 1 can have the standard deviation of the differencesbetween the respective positions of the vertexes of the convexities 131in the normal direction of the flat surface 12 of the base material 11and the median of the positions of the vertexes of the convexities 131greater than or equal to 35 nm.

In addition, the pulse signal illustrated in (C) of FIG. 6 is a pulsesignal obtained by performing random phase modulation on a rectangularwave having a period of P and a pulse width of D. Phase modulation is tovary timings of risings of a waveform in periods, and a phase-modulatedpulse signal has varied timings of risings and falls of a waveform withrespect to the pulse signal illustrated in (A) of FIG. 6, as illustratedin (C) of FIG. 6.

In a case in which the control mechanism 47 generates the pulse signalillustrated in (C) of FIG. 6, for example, lengths of non-irradiationtimes randomly vary in accordance with a phase modulation amount whilelength of irradiation times of the laser light 30 are uniform. Thus,since the sizes of the regions not thermally reacting due to exposurerandomly vary depending on positions of the latent images 23A, the sizesof the regions not thermally reacting due to exposure randomly varydepending on a phase modulation amount of the pulse signal used inexposure of the adjacent latent images 23A. Thus, in the developedresist layer, the sizes of the regions in which the resist remainsrandomly vary depending on the phase modulation amount of the pulsesignal used in exposure of adjacent resist patterns, and thereby theconvexities having uneven heights are formed on the master base material21 through etching.

Note that, in the case in which the control mechanism 47 generates thepulse signal illustrated in (C) of FIG. 6, the lengths of theirradiation times of the laser light 30 are uniform, and thus a planararray of the concave-convex structure 23 formed on the master basematerial 21 is a substantially periodic array, rather than a randomarray.

In addition, in the case in which the control mechanism 47 generates therandomly phase-modulated pulse signal illustrated in (C) of FIG. 6, theexposure device 3 can control the uneven degree of the positions of thebottom faces of the concavities and the positions of the vertexes of theconvexities of the concave-convex structure 23 in the normal directionof the outer circumferential surface of the master base material 21 byvarying the phase modulation amount of the pulse signal.

That is, in the present embodiment, it is possible to control unevennessin the position of the bottom faces of the concavities and unevenness inthe positions of the vertexes of the convexities in the normal directionof the flat surface of the base material of the optical body 1 producedusing the master 2 by controlling a phase modulation amount of a pulsesignal that controls oscillation made by the laser light source 31 thatis used in the production of the master 2.

In the case of the optical body 1 in which the standard deviation of thedifferences between the respective positions of the bottom faces of theconcavities 133 in the normal direction of the flat surface of the basematerial of the optical body 1 and the median of the positions of thebottom faces of the concavities 133 is greater than or equal to 25 nm asdescribed above, for example, a phase modulation amount of a pulsesignal may be greater than or equal to 10% of the period of the pulsesignal. In addition, in the case of in the optical body 1 in which thestandard deviation of the differences between the respective positionsof the vertexes of the convexities 131 in the normal direction of theflat surface of the base material of the optical body 1 and the medianof the positions of the vertexes of the convexities 131 is greater thanor equal to 35 nm as described above, a phase modulation amount of apulse signal may be greater than or equal to 10% of a period of thepulse signal.

As described above, randomness of a certain degree is imparted to apulse signal controlling irradiation of the laser light 30 in theexposure process of forming patterns on the outer circumferentialsurface of the master 2 for producing the optical body 1 according tothe present embodiment. Accordingly, the positions of the bottom facesof the concavities and the positions of the vertexes of the convexitiesof the concave-convex structure 23 of the master 2 can have unevennessof a certain degree. Therefore, the above-described master 2 can producethe optical body 1 according to the present embodiment by transferringthe concave-convex structure 23 formed on the outer circumferentialsurface to a resin or the like.

Here, the exposure of the columnar or cylindrical master base material21 to light can be executed by, for example, the exposure device 3 thatwill be described in detail with reference to FIG. 7. FIG. 7 is anexplanatory diagram for describing a specific configuration of theexposure device 3 used in the exposure of the master base material 21 tolight.

The exposure device 3 includes the laser light source 31, a first mirror33, a photodiode (PD) 34, a condenser lens 36, an electro-opticdeflector (EOD) 39, a collimator lens 38, a second mirror 41, a beamexpander (BEX) 43, and an objective lens 44 as illustrated in FIG. 7. Inaddition, the laser light source 31 is controlled by the controlmechanism 47, and the laser light 30 oscillating from the laser lightsource 31 is irradiated to the master base material 21 placed on aturntable 46 rotated by a spindle motor 45.

The laser light source 31 is a light source that causes the laser light30 exposed to the resist layer formed on the outer circumferentialsurface of the master base material 21 to oscillate as described above.The laser light source 31 may be a semiconductor laser that emits laserlight having a wavelength in the range from 400 nm to 500 nm, forexample, the blue light band. The laser light 30 released from the laserlight source 31 travels straight ahead as a parallel beam and then isreflected on the first mirror 33.

In addition, the laser light 30 reflected on the first mirror 33 iscondensed at the electro-optic deflector 39 by the condenser lens 36,and then turns into a parallel beam again by the collimator lens 38. Thelaser light 30 that has turned into a parallel beam is reflected on thesecond mirror 41 and then horizontally led onto a moving optical table42.

The first mirror 33 is configured as a polarization beam splitter andhas a function of reflecting some of polarized light components thereonand transmitting the other polarized light components therethrough. Thepolarized light components transmitted through the first mirror 33 arephotoelectrically converted by the photodiode 34, and aphotoelectrically converted light receiving signal is input to the laserlight source 31. Accordingly, the laser light source 31 can controloutput adjustment of the laser light 30 or the like on the basis offeedback by the input light receiving signal.

The electro-optic deflector 39 is an element that can controlirradiation positions of the laser light 30 to be in a distance ofnanometers or so. The exposure device 3 can finely adjust irradiationpositions of the laser light 30 irradiated onto the master base material21 using the electro-optic deflector 39.

The moving optical table 42 includes the beam expander 43 and theobjective lens 44. The laser light 30 led onto the moving optical table42 is adjusted to have a desired beam shape by the beam expander 43, andthen radiated onto the resist layer formed on the outer circumferentialsurface of the master base material 21 via the objective lens 44.

Here, while the master base material 21 is rotated using the turntable46, the laser light 30 is moved in the axial direction (i.e., thedirection of the arrow R) of the master base material 21, the laserlight 30 is intermittently radiated onto the resist layer, and therebylight exposure is performed on the master base material 21. Movement ofthe irradiation positions of the laser light 30 may be performed inaccordance with movement of the turntable 46, or performed in accordancewith movement of a laser head including the laser light source 31.

In addition, the exposure device 3 includes the control mechanism 47that controls irradiation times and irradiation positions of the laserlight 30. The control mechanism 47 includes a formatter 48 and a driver49 and controls irradiation times and irradiation positions of the laserlight 30.

The driver 49 controls oscillation made by the laser light source 31 onthe basis of a pulse signal having randomness generated by the formatter48. In addition, the driver 49 synchronizes a pulse signal from theformatter 48 with a servo signal of the spindle motor 45 on eachcircumference so that light-exposed two-dimensional arrays aresynchronized with each other on every circumference in the axialdirection of the master base material 21. With the above-configuredexposure device 3, pattern formation is performed on the master basematerial 21.

The master base material 21 exposed to light by the exposure device 3can be used to produce the master 2 having the concave-convex structure23 formed on the outer circumferential surface by going through thedevelopment process and the etching process as described above. Throughthe transfer of the master 2 produced as described above, the opticalbody 1 according to the present embodiment can be efficiently produced.Specifically, by using a transfer device 5 illustrated in FIG. 8, theoptical body 1 onto which the concave-convex structure 23 formed on theouter circumferential surface of the master 2 is transferred can becontinuously produced.

The transfer device 5 for producing the optical body 1 according to thepresent embodiment will be described as follows with reference to FIG.8. FIG. 8 is a schematic diagram illustrating a configuration of thetransfer device 5 for producing the optical body 1 according to thepresent embodiment.

As illustrated in FIG. 8, the transfer device 5 includes the master 2, abase material supply roll 51, a winding roll 52, guide rolls 53 and 54,a nip roll 55, a separating roll 56, a coating device 57, and a lightsource 58. That is, the transfer device 5 illustrated in FIG. 8 is aroll-to-roll nano-imprinting transfer device.

The base material supply roll 51 is, for example, a roll in which thebase material 11 in a sheet form is wound in a roll shape, and thewinding roll 52 is a roll to wind the optical body 1 in which a resinlayer 62 onto which the concave-convex structure 23 (i.e., an invertedstructure of the micro concave-convex structure 13) has been transferredis laminated. In addition, the guide rolls 53 and 54 are rolls totransport the base material 11 that has not gone through a transfer orthe optical body 1. The nip roll 55 is a roll to press the base material11 on which the resin layer 62 has been laminated onto the master 2, andthe separating roll 56 is a roll to separate the optical body 1 on whichthe resin layer 62 has been laminated from the master 2 after theconcave-convex structure 23 is transferred to the resin layer 62.

The coating device 57 includes a coating means such as a coater andcoats a photocurable resin composition onto the base material 11 to formthe resin layer 62. The coating device 57 may be, for example, a gravurecoater, a wire bar coater, or a die coater, or the like. In addition,the light source 58 is a light source that emits light having awavelength at which a photocurable resin composition can harden, and maybe, for example, an ultraviolet lamp or the like. Note that the resinlayer 62 may be formed of a thermosetting resin composition.

Note that the photocurable resin composition is a resin that hardenswhen light having a predetermined wavelength is radiated thereto.Specifically, the photocurable resin composition may be a UV curableresin such as acrylic resin acrylate or epoxy acrylate. In addition, thephotocurable resin composition may contain an initiator, a filler, afunctional additive, a solvent, an inorganic material, a pigment, anantistatic agent, a sensitizing dye, or the like if necessary.

In the transfer device 5, first, the base material 11 is consecutivelysent out from the base material supply roll 51 via the guide roll 53.The coating device 57 coats the photocurable resin composition on thesent base material 11 to laminate the resin layer 62 on the basematerial 11. In addition, the base material 11 on which the resin layer62 has been laminated is pressed to the master 2 by the nip roll 55.Accordingly, the concave-convex structure 23 formed on the outercircumferential surface of the master 2 is transferred to the resinlayer 62. The resin layer 62 to which the concave-convex structure 23has been transferred hardens through irradiation of light from the lightsource 58. Accordingly, the micro concave-convex structure 13 is formedon the resin layer 62. The optical body 1 on which the microconcave-convex structure 13 has been formed is separated from the master2 by the separating roll 56 and sent out to the winding roll 52 via theguide roll 54 to be wound.

With the above-described transfer device 5, the optical body 1 with themicro concave-convex structure 13 formed on the surface by transferringthe concave-convex structure 23 formed on the outer circumferentialsurface of the master 2 thereto can be efficiently produced.

EXAMPLES

The optical body according to the present embodiment will be describedbelow in more detail with reference to Examples and Comparative Examplesthereof. Note that Example that will be introduced below is merely acondition example to show feasibility and an effect of the optical bodyand a manufacturing method thereof according to the present embodiment,and the optical body and the manufacturing method thereof according tothe present invention is not limited to the following examples.

First Experiment Examples Example 1

An optical body according to Example 1 was produced in the followingprocess. First, a resist layer was formed of a material containingtungsten oxide on an outer circumferential surface of a master basematerial (a length in an axial direction of 480 mm×an outer diameter of132 mm), which is formed of cylindrical quartz glass, to have athickness of about 50 to 60 nm using the sputtering method. Next,thermal reaction lithography with laser light was performed using anexposure device to form latent images on the resist layer.

Exposure patterns were arranged such that circular dots were arranged toform rows (tracks) at each pitch of about 230 nm in the circumferentialdirection of the master base material and to have a hexagonal grid shapein which an interval between adjacent dots is about 150 nm (i.e.,adjacent tracks alternately deviate by a half pitch). Exposure wasperformed using a pulse signal obtained by further randomlyphase-modulating a rectangular wave used for exposure of the exposurepatterns (having a frequency of 27 MHz and a duty ratio of 60%) at 17%of a period.

Next, by performing development processing on the exposed master basematerial using NMD 3 (2.38 mass % of a tetramethylammonium hydroxideaqueous solution) (manufactured by Tokyo Ohka Kogyo Co., Ltd.), theresist on which the latent images had been formed was dissolved, andthereby a dot-arrayed concave-convex structure was formed on the resistlayer. Next, reactive ion etching (RIE) was performed using CHF₃ gas (30sccm) at gas pressure of 0.5 Pa with input power of 200 W to etch themaster base material for 60 to 120 minutes using the resist layer as amask.

In the above-described process, the master with the concave-convexstructure formed on the outer circumferential surface was produced.Furthermore, the optical body was produced using the produced master.Specifically, the concave-convex structure formed on the outercircumferential surface of the master was transferred to a UV curableresin using the transfer device and thereby the optical body accordingto Example 1 was produced. In addition, a polyethylene terephthalatefilm was used for the base material of the optical body, and the UVcurable resin hardened through irradiation of ultraviolet rays of 1000mJ/cm² from a metal halide lamp for 1 minute. Note that a planar arrayof convexities or concavities of the produced optical body was asubstantially hexagonal array.

Example 2

A master was produced using a similar method to that of Example 1 exceptthat a phase modulation amount of a pulse signal used in exposure wasset to 11% of a period. In addition, an optical body to which theconcave-convex structure formed on an outer circumferential surface ofthe master was transferred was produced using the similar method to thatof Example 1. Note that a planar array of convexities or concavities ofthe produced optical body was a substantially hexagonal array.

Example 3

A master was produced using a similar method to that of Example 1 exceptthat a period and a duty ratio of a pulse signal used in exposure wererandomly modulated. In addition, an optical body to which theconcave-convex structure formed on an outer circumferential surface ofthe master was transferred was produced using the similar method to thatof Example 1. Note that a planar array of convexities or concavities ofthe produced optical body was a random array.

Comparative Example 1

A master was produced using a similar method to that of Example 1 exceptthat a pulse signal used in exposure was not phase-modulated and wasused as a periodic signal. In addition, an optical body to which theconcave-convex structure formed on an outer circumferential surface ofthe master was transferred was produced using the similar method to thatof Example 1. Note that a planar array of convexities or concavities ofthe produced optical body was a hexagonal array.

Comparative Example 2

A master was produced using a similar method to that of Example 1 exceptthat a phase modulation amount of a pulse signal used in exposure wasset to 8% of a period. In addition, an optical body to which theconcave-convex structure formed on an outer circumferential surface ofthe master was transferred was produced using the similar method to thatof Example 1. Note that a planar array of convexities or concavities ofthe produced optical body was a substantially hexagonal array.

(Evaluation Result)

Surface shapes of the optical bodies according to Examples 1 to 3 andComparative Examples 1 and 2 produced as described above were evaluatedusing an atomic force microscope (AFM). A perspective diagram of thesurface shape of the optical body according to Example 2 measured usingthe AFM is illustrated in FIG. 9 as a representative example.

Note that the surface shape of a region of 2 square μm of the opticalbody was measured using SPA 400 (manufactured by Hitachi High-TechScience Corporation) for the AFM in a dynamic focus mode at a scan speedof 0.7 Hz. As a probe, SI-DF40P2 having a tip curvature radius of 7 nmand a spring constant of 26 N/m was used.

It can be ascertained referring to FIG. 9 that the optical bodyaccording to Example 2 has convexities periodically arrayed in atwo-dimensional hexagonal grid array. In addition, it is ascertainedthat heights of the convexities are not uniform and are uneven at eachconvexity.

In addition, straight lines passing through the respective vertexes ofconvexities were extracted from central tracks of a measurement regionof each of the optical bodies and cross-sectional shapes of the opticalbodies having the straight lines as cutting lines were calculated. Inthe above-described calculation method, the heights of the convexities,the standard deviation of the differences between positions of thevertexes and the median of the positions of the vertexes of theconvexities, and the standard deviation of the differences between thepositions of the bottom faces and the median of the positions of thebottom faces of the concavities were calculated using the calculatedcross-sectional shape. The calculation results are shown in Table 1below.

Next, optical characteristics of the optical bodies according toExamples 1 to 3 and Comparative Examples 1 and 2 were evaluated using aspectrophotometer. The evaluation results are shown in Table 1 below.

Note that V550 (manufactured by JASCO Corporation) was used as thespectrophotometer, and ARV474S (manufactured by JASCO Corporation) wasused as an absolute reflectance measuring instrument. In a regularreflection measurement mode, regular reflection of incident light at anangle of 5° was measured at a wavelength resolution of 1 nm in the rangefrom 350 nm to 800 nm. The result thereof is shown in FIG. 10. FIG. 10is a graph chart in which reflectances of the optical bodies accordingto Examples 1 to 3 and Comparative Examples 1 and 2 are evaluated ateach wavelength of incident light.

In addition, luminous reflectance (which will also be referred to as a Yvalue) and reflection hues (a*, b*) were calculated using a tone ofregular reflection light. Here, the luminous reflectance (Y value) is(Y, x, y) when the color of the regular reflection light is expressed inthe Yxy color system and represents that regular reflection issuppressed further as the luminous reflectance (Y value) becomessmaller. In addition, the reflection hues (a*, b*) are (L*, a*, b*) whenthe color of reflected light is expressed in a L* a* b* color system andrepresent that reflected light is closer to white with lesser color asthe values of the reflection hues (a*, b*) get closer to 0.

Note that, in Table 1, the “unevenness in concavities” represents thestandard deviation of the differences between the respective positionsof the bottom faces of the concavities in the normal direction of theflat surface of the base material and the median of the positions of thebottom faces, and the “unevenness in convexities” represents thestandard deviation of the differences between the respective positionsof the vertexes of the convexities in the normal direction of the flatsurface of the base material and the median of the positions of thevertexes.

[Table 1]

TABLE 1 Comparative Comparative example 1 Example 1 Example 2 Example 3example 2 Pulse signals Periodic Phase Phase Random Phase signalmodulation modulation signal modulation at 17% of at 11% of at 8% ofperiod period period Heights of 254.9 202.8 225.6 244.4 252.5convexities [nm] Unevenness 6.5 50.3 31.3 47.2 16.6 in concavities [nm]Unevenness 9.5 43.1 38.8 46.7 32.7 in convexities [nm] Averagereflectance 0.42 0.12 0.12 0.11 0.30 in the range from 380 to 780 nm [%]Y value[%] 0.54 0.11 0.12 0.09 0.35 a* −2.21 −0.02 −0.16 0.23 −0.86 b*1.33 0.24 0.26 0.14 1.63

Referring to Table 1 and FIG. 10, it is ascertained that the opticalbodies according to Examples 1 to 3 have unevenness (standard deviation)in the concavities greater than or equal to 25 nm and reflectancesthereof are low through the wavelength band from 350 nm to 800 nm. Onthe other hand, it is ascertained that the optical bodies according toComparative Examples 1 and 2 have unevenness (standard deviation) in theconcavities less than 25 nm and thus reflectances thereof areparticularly higher in the wavelength band from 450 nm to 600 nm than inother wavelength bands. Therefore, it is ascertained that the opticalbodies according to Examples 1 to 3 have the absolute values of thereflection hues a* and b* smaller than those in Comparative Examples 1and 2 to be equal to or smaller than 1 and thus reflected light has nocolor.

In addition, it is ascertained that the optical bodies according toExamples 1 to 3 have average reflectances in the range from 380 nm to780 nm and luminous reflectances (Y values) that are lower than those ofthe optical bodies according to Comparative Examples 1 and 2 and bothare equal to or lower than 0.2%. Therefore, it is ascertained that theoptical bodies according to Examples 1 to 3 can suppress reflection morethan the optical bodies according to Comparative Examples 1 and 2.

Here, correlations between the unevenness in the concavities and Yvalues that are the luminous reflectances of Examples 1 to 3 andComparative Examples 1 and 2 are illustrated in FIG. 11. FIG. 11 is ascatter diagram in which the horizontal axis represents the standarddeviation of the differences between the positions of the bottom facesand the median of the positions of the bottom faces of the concavitiesof each optical body and the vertical axis represents the Y value.

As illustrated in FIG. 11, it is ascertained that the Y value decreasesas the unevenness in the positions of the bottom faces of theconcavities in the normal direction of the flat surface of the opticalbody becomes greater and thus reflection can be further suppressed. Inaddition, it is ascertained that, in the case in which the standarddeviation is greater than or equal to 25 nm, the decrease of the Y valuedue to the increasing unevenness in the positions of the bottom faces ofthe concavities in the normal direction of the flat surface of theoptical body reaches saturation. Therefore, it is ascertained withrespect to the optical body according to the present embodiment that theY value that is a luminous reflectance can be dramatically reduce bysetting the standard deviation of the positions of the bottom faces ofthe concavities in the normal direction of the flat surface of theoptical body to be greater than or equal to 25 nm.

Second Experiment Examples Example 4

An optical body according to Example 4 was produced in the followingprocess. First, similarly to Example 2, formation or a resist, lightexposure, and development were performed on a master base material toform the concave-convex structure (i.e., the micro concave-convexstructure) on a resist layer. Note that a phase modulation amount of apulse signal used in the exposure was set to 11% of a period.

Next, an inorganic resist layer formed of SiO₂ was formed on the resistlayer on which the micro concave-convex structure has been formed tohave a thickness of 1000 nm. Note that the inorganic resist layer wasformed through oxygenated sputtering using a Si target. Successively,using a diluted solution of P4210 that is a novolac resin (manufacturedby AZ) with acetone at a ratio of 20 times (mass ratio), atomized P4210was sprayed on the inorganic resist layer through spray coating.Accordingly, an organic resist layer having the macro concave-convexstructure was formed on the inorganic resist layer. Note that an averageperiod of concavities and convexities of the macro concave-convexstructure was approximately longer than or equal to 1 μm, which waslonger than a wavelength belonging to the visible light band.

Thereafter, reactive ion etching was performed using CHF₃ gas (30 sccm)and CHF₄ gas (30 sccm) at gas pressure of 0.5 Pa with input power of 200W to etch the inorganic resist layer for 30 minutes using the organicresist layer as a mask. Next, reactive ion etching was performed usingCHF₃ gas (30 sccm) at gas pressure of 0.5 Pa with input power of 200 Wto etch the master base material for 60 to 120 minutes using theinorganic resist layer and the resist layer as masks.

Through the above-described process, a master on which the macroconcave-convex structure and the micro concave-convex structure wereformed in a superimposing manner was produced on an outercircumferential surface. Furthermore, an optical body was produced usingthe produced master in a similar method to that of Example 1.

Comparative Example 3

A master was produced in a similar method to that of Example 4 exceptthat a pulse signal used in exposure was used as a periodic signalwithout change with no phase modulation. In addition, an optical bodywas produced using the produced master in a similar method to that ofExample 1.

(Evaluation Result)

Next, reflectances of the optical bodies according to Example 4 andComparative Example 3 were evaluated using a spectrophotometer. Notethat similar measurement method and measurement device for reflectancesto those of the first experiment example were used. The evaluationresults are shown in FIG. 12. FIG. 12 is a graph chart in whichreflectances of the optical bodies according to Example 4 andComparative Example 3 are evaluated at each wavelength of incidentlight.

As illustrated in FIG. 12, it is ascertained that, even if the opticalbody according to Example 3 is an optical body in which the macroconcave-convex structure of which the average period of the concavitiesand convexities is longer than wavelengths belonging to the visiblelight band is superimposed on the micro concave-convex structure ofwhich the average period of the concavities and convexities is equal toor shorter than wavelengths belonging to the visible light band, theoptical body according to Example 3 can further reduce a reflectancethrough the wavelength band from 350 nm to 800 nm than the optical bodyaccording to Comparative Example 4. Since the optical body according toExample 3 has a reflectance reduction effect attributable to the microconcave-convex structure and an antiglare effect attributable to themacro concave-convex structure, the optical body can dramaticallyimprove visibility of a display plane of a display device or the likewhen the optical body is used for the display plane.

As described above, the optical body 1 according to the presentembodiment can suppress reflection of incident light beams havingvarious wavelengths by increasing unevenness in the positions of thebottom faces of the concavities 133 of the micro concave-convexstructure 13 in the normal direction of the flat surface 12 of the basematerial 11. Thus, by reducing the wavelength dependence of areflectance, the optical body 1 according to the present embodiment canlower the reflectance over a wide wavelength band. Accordingly, theoptical body 1 according to the present embodiment can prevent reflectedlight from having color.

Since the optical body 1 according to the present embodiment has lowwavelength dependence and a lower reflectance, the optical body candramatically improve visibility of a display plane of a display deviceor the like, for example, when the optical body is used for the displayplane.

The preferred embodiment(s) of the present invention has/have beendescribed above with reference to the accompanying drawings, whilst thepresent invention is not limited to the above examples. A person skilledin the art may find various alterations and modifications within thescope of the appended claims, and it should be understood that they willnaturally come under the technical scope of the present invention.

REFERENCE SIGNS LIST

-   1 optical body-   2 master-   11 base material-   12 flat surface-   13 micro concave-convex structure-   14 macro concave-convex structure-   21 master base material-   23 concave-convex structure-   131 convexity-   133 concavity-   141 peak-   143 valley

The invention claimed is:
 1. An optical body comprising: aconcave-convex structure formed on a surface of a base material, whereinan average period of concavities and convexities of the concave-convexstructure is equal to or shorter than a wavelength belonging to avisible light band, a standard deviation of differences betweenrespective positions of bottom faces of all the concavities of theconcave-convex structure in a normal direction of a flat surface of thebase material and a median of the positions of all the bottom faces isgreater than or equal to 25 nm, and a standard deviation of differencesbetween respective positions of vertexes of all the convexities of theconcave-convex structure in the normal direction of the flat surface ofthe base material and a median of the positions of all the vertexes isgreater than or equal to 35 nm.
 2. The optical body according to claim1, wherein a Y value that is a luminous reflectance of the optical bodyis equal to or lower than 0.2%, and the absolute values of reflectionhues a* and b* of the optical body are equal to or smaller than
 1. 3.The optical body according to claim 1, wherein an average reflectance ofthe optical body in a wavelength band from 380 nm to 780 nm is equal toor lower than 0.2%.
 4. The optical body according to claim 1, furthercomprising: a macro concave-convex structure formed on the surface ofthe base material to be superimposed on the concave-convex structure,wherein an average period of concavities and convexities of the macroconcave-convex structure is longer than a wavelength belonging to thevisible light band.
 5. The optical body according to claim 1, wherein aplanar array of the convexities or concavities of the concave-convexstructure is a hexagonal grid shape or a square grid shape.
 6. Theoptical body according to claim 1, wherein a planar array of theconvexities or concavities of the concave-convex structure is a randomarray.
 7. A display device comprising: the optical body according toclaim
 1. 8. The optical body according to claim 1, wherein respectivepositions of the bottom faces of the concavities of the concave-convexstructure in the normal direction of the flat surface of the basematerial vary randomly, and respective positions of the vertexes of theconvexities of the concave-convex structure in the normal direction ofthe flat surface of the base material vary randomly.
 9. The optical bodyaccording to claim 1, wherein the standard deviation of differencesbetween respective positions of the bottom faces of the concavities ofthe concave-convex structure in the normal direction of the flat surfaceof the base material and the median of the positions of the bottom facesis greater than or equal to 25 nm and less than or equal to 200 nm, andthe standard deviation of differences between respective positions ofthe vertexes of the convexities of the concave-convex structure in thenormal direction of the flat surface of the base material and the medianof the positions of the vertexes is greater than or equal to 35 nm andless than or equal to 200 nm.